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Date: Thu, 01 Oct 2020 00:09:48 -0700
From: Paul Johnson via groups.io <pjpolliwog=<yahoo.com...>
Subject: Re: [NorWestLeps] San Francisco butterflies breeding times

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I don't know enough about the butterflies in your area (or mine) to answer =
your Vanessa question definitively.=C2=A0 Maybe nobody does.

Here's some food for thought, based somewhat on speculation...

When we speak about animal behavior, we are often speaking in generalities=
.=C2=A0 It's not that all individuals of a species act a certain way.=C2=A0=
It's more of a probability that an individual will act a certain way.

So, for example, we can say that the Monarchs that return to California in=
the fall have entered reproductive diapause, and will not start breeding u=
ntil late winter or early spring.=C2=A0 But every once in a while, we'll se=
e a mating pair of Monarchs in October.=C2=A0 So maybe 99% of Monarchs foll=
ow the pattern.=C2=A0 What determines that 99% number?=C2=A0 Is it affected=
by environmental factors such as weather or larval food conditions?=C2=A0 =
Or is in inborn, genetically based?=C2=A0 Even if it's inborn, it's possibl=
e that natural selection can change it over the years, so that if environme=
ntal changes favor breeding in the fall, over the years we may see more and=
more Monarchs breeding then.=C2=A0 So even if we "know" something about wh=
at a species does in SF this year, that might have little bearing on what t=
hey do in 10 years or 50 years.=C2=A0 And this ratio might also vary geogra=
phically.

We need to remember that butterflies probably can't predict the future, an=
d they're probably not adopting a particular strategy because they think it=
's going to work.=C2=A0 More likely, individual butterflies are predetermin=
ed to behave a certain way, and there is some variation between individuals=
.=C2=A0 Often what we probably see is that the strategy followed by most in=
dividuals in an area is the one that works most of the time, and strategies=
followed by fewer individuals fail most of the time, but in some years the=
se "failure" strategy followers are successful when the majority's strategy=
fails.=C2=A0 The butterflies have no idea whether their strategy will work=
.=C2=A0 They just live their lives the way they are programmed to, and some=
survive while others do not.=C2=A0 Those that survive pass their genes alo=
ng to the next generation.

Here's a completely made up example...

There is a butterfly called the California Lady that ranges from the Bay A=
rea to San Diego.=C2=A0 Its native host plants are gumweeds.=C2=A0 Now it t=
urns out that gumweeds can survive the winter in San Diego, but in the SF B=
ay Area the winters are so cold that gumweeds only survive as seeds.=C2=A0 =
Throughout their range, the butterflies can pass the winter as a caterpilla=
r or an adult, but the caterpillars only make it if they have plenty of fre=
sh gumweed to eat.=C2=A0 And overwintering adults are highly prone to attac=
k by ants as they hide out in cracks and crevices to shelter against cold w=
inter nights.

Now a detailed life history study from 1990-2000 found that in San Diego, =
90% of individuals overwinter as caterpillars and 10% overwinter as adults.=
=
=C2=A0 Once every decade, a very cold winter kills off the gumweed and the=
overwintering caterpillars all starve to death, while some of the overwint=
ering adults survive, despite many of them being eaten by ants.=C2=A0 Even =
though overwintering as a caterpillar is the successful strategy in Sand Di=
ego in most years, in very cold years the strategy of overwintering as an a=
dult is what keeps the species from being wiped out locally.=C2=A0 So it pa=
ys to have some outliers in the population, even though most years they fai=
l.

The same 1990-2000 study found that SF Bay Area California Lady butterflie=
s have the opposite strategy.=C2=A0 90% of individuals overwinter as adults=
and 10% as caterpillars.=C2=A0 In 9 out of 10 winters, the cold weather ki=
lls off the gumweed and all the overwintering caterpillars starve to death.=
=
=C2=A0 Only the overwintering adults survive the winter.=C2=A0 But once pe=
r decade, an unusually warm winter allows the gumweed to live through the w=
inter, and the overwintering caterpillars do much better than the overwinte=
ring adults, which get devoured by the ants, which are more active than usu=
al on the warmer nights.=C2=A0 So here, overwintering as an adult is usuall=
y the winning strategy, but in very warm years it's the overwintering cater=
pillars that keep the species from being wiped out locally.=C2=A0 Again, it=
pays to have some outliers in the population, even though they fail in mos=
t years.

The study was repeated in 2010-2020, but something had changed: Guernsey G=
umweed was introduced to California and although it did not do well in the =
face of competition from natives gumweeds in natural areas, it thrived in c=
ities.=C2=A0 The thing about Guernsey Gumweed is that it does quite well in=
Bay Area winters.=C2=A0 So what did the study find?=C2=A0 Things hadn't ch=
anged in San Diego: overwintering caterpillars were still the most successf=
ul strategy in most years.=C2=A0 And in natural areas in the East Bay Hills=
, they found the same results as in the previous study: overwintering adult=
s were the most successful in most years.=C2=A0 But in SF where Guernsey Gu=
mweed was well-established and supported caterpillars through most winters,=
overwintering California Lady caterpillars became the dominant strategy, j=
ust like in San Diego.

The study was then put on hold indefinitely because, after all, it was 202=
0.=C2=A0 But then in 2100-2110 it was repeated.=C2=A0 By then SF Bay area t=
emperatures had warmed by a few degrees, allowing native gumweeds to surviv=
e the winter in all but the coldest years.=C2=A0 And in San Diego, winter t=
emperatures were so warm that gumweeds never died off, not even in the cold=
est winters.=C2=A0 So what did the study find?=C2=A0 In San Diego, the over=
wintering adults had all but disappeared.=C2=A0 Every individual found in w=
inter was a caterpillar.=C2=A0 The same was true in SF, where the introduce=
d Guernsey Gumweed supported overwintering caterpillars even through the co=
ldest winters, and no overwintering adults could be found.=C2=A0 What about=
in the natural areas in the East Bay Hills, where the native gumweeds made=
it through 9 out of 10 winters?=C2=A0 There, the species had adopted the f=
ormer San Diego scenario, in which 90% of California Ladies overwintered as=
caterpillars and only 10% as adults.

Now, imagine if someone asked the question: Do California Ladies overwinte=
r as caterpillars or adults?=C2=A0 The answer would depend not only on the =
location, but also the year.=C2=A0 Even back in the 1990s, the answer depen=
ded on the year, with most years favoring overwintering caterpillars, but 1=
out of 10 years favoring overwintering adults.=C2=A0 Also, if someone had =
seen a California Lady in San Diego in June of 1995 and asked whether its o=
ffspring would overwinter as adults or caterpillars, you wouldn't have been=
able to answer definitively, although you could have said that there's a 9=
0% chance they will overwinter as caterpillars and a 10% chance they'll ove=
rwinter as adults.

Now back to the real world: Do American Ladies in SF breed in September?=
=C2=A0 How many butterflies would we need to observe to answer that questi=
on, and over how many years?=C2=A0 And if we had studied them in the East B=
ay Hills, could we apply our results to the same species living in SF?=C2=
=A0 Or if we had studied them before the arrival of the non-native cudweed=
, would our results still apply after the cudweed had been established for =
a while?=C2=A0 Will our results still apply as average temperatures change?

Forgetting all of that for a moment, there are other reasons why answering=
the "breeding season(s)" question may be difficult...

For butterflies with multiple generations per year (all Vanessas in SF?), =
the timing of those generations may vary each year, and they may not always=
be in sync.=C2=A0 (The following example is made up.)=C2=A0 Maybe one Vane=
ssa species usually breeds in April (1st generation), June (2nd generation)=
, and August (3rd generation), and then goes into reproductive diapause unt=
il April.=C2=A0 But in an especially warm year, maybe that's March, May, an=
d July.=C2=A0 And maybe some of those July butterflies do breed and have a =
generation that emerges in September and then diapauses through the winter.=
=
=C2=A0 And maybe in a cold year they start in May and only get two generat=
ions in that year.

Some butterflies have partial generations.=C2=A0 For example, Sara Orange-=
tips apparently have a full generation that flies in early spring, and some=
of their offspring emerge in late spring while others wait until the follo=
wing spring to emerge.=C2=A0 So their "breeding periods" may be easy to ide=
ntify, but only some individuals are breeding during the second breeding pe=
riod.

Butterflies may have their life histories in sync with the life history of=
their local host plant, which may vary over small geographic scales.=C2=A0=
For example, Anise Swallowtails living in towns have been shown to have mo=
dified the timing of their life history to match the timing of non-native F=
ennel, while Anise Swallowtails in nearby natural areas retain their natura=
l phenology.=C2=A0 So the breeding seasons of Anise Swallowtails can be dif=
ferent in areas just a few miles apart.

And as another example, I suspect that the Variable Checkerspots in my are=
a have such a long flight season because their caterpillars feed on at leas=
t three different plants, each of which grows in a different microclimate a=
nd has a different phenology.=C2=A0 So when defining the breeding season fo=
r this species, should we separate out each host plant cohort, or should we=
just lump them all together?

I don't have any real data on this, but I have wondered about the Red Admi=
rals I can find hilltopping on just about any warm winter day.=C2=A0 The pu=
rpose of hilltopping is mating.=C2=A0 Males go to hilltops to wait for rece=
ptive females to arrive, and then they mate.=C2=A0 So if I see male Red Adm=
irals on hilltops, it must be their breeding season, right?=C2=A0 Maybe not=
.=C2=A0 Perhaps males are just covering their bases: any day that's warm en=
ough to fly, they'll head for a nearby hilltop just in case a receptive fem=
ale might arrive.=C2=A0 But maybe females won't emerge and head for hilltop=
s until March.=C2=A0 If that's the case, then even though males appear to b=
e ready to breed all winter long, I don't think it's really breeding season=
until receptive females join them.=C2=A0 But let's remember that there are=
often some outliers that don't follow the "normal" pattern.=C2=A0 What if =
1% of females are receptive throughout the winter and will fly to hilltops =
on warm winter days to mate?=C2=A0 Does that 1% make winter into Red Admira=
l breeding season?=C2=A0 What if 10% of female Red Admirals breed in winter=
?=C2=A0 50%?=C2=A0 How do we determine what percentage of butterflies in br=
eeding status is required to call it breeding season?

These examples are meant to convey some of the complexities of determining=
the breeding season(s) of butterfly species.=C2=A0 Every species is differ=
ent, and there may be complications, variability, local variation, evolutio=
n, etc.=C2=A0 And definitions of "breeding season" may not be as straightfo=
rward as we would hope.

I hope this helps!

I encourage folks to photograph butterflies nectaring, breeding, laying eg=
gs, etc. and post their observations on iNaturalist.=C2=A0 The more of thes=
e observations get posted, the more data will be available to investigate t=
hese kinds of questions.

Thanks,

Paul
--
Paul G. Johnson
Paicines, CA
<pjpolliwog...> ( pjpolliwog@yahoo, )


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I don't know enough about the butterflies in your area (or mine) to answer =
your Vanessa question definitively.&nbsp; Maybe nobody does.&nbsp; <br /><b=
r />Here's some food for thought, based somewhat on speculation...<br /><br=
/>When we speak about animal behavior, we are often speaking in generaliti=
es.&nbsp; It's not that all individuals of a species act a certain way.&nbs=
p; It's more of a probability that an individual will act a certain way.&nb=
sp; <br /><br />So, for example, we can say that the Monarchs that return t=
o California in the fall have entered reproductive diapause, and will not s=
tart breeding until late winter or early spring.&nbsp; But every once in a =
while, we'll see a mating pair of Monarchs in October.&nbsp; So maybe 99% o=
f Monarchs follow the pattern.&nbsp; What determines that 99% number?&nbsp;=
Is it affected by environmental factors such as weather or larval food con=
ditions?&nbsp; Or is in inborn, genetically based?&nbsp; Even if it's inbor=
n, it's possible that natural selection can change it over the years, so th=
at if environmental changes favor breeding in the fall, over the years we m=
ay see more and more Monarchs breeding then.&nbsp; So even if we "know" som=
ething about what a species does in SF this year, that might have little be=
aring on what they do in 10 years or 50 years.&nbsp; And this ratio might a=
lso vary geographically.<br /><br />We need to remember that butterflies pr=
obably can't predict the future, and they're probably not adopting a partic=
ular strategy because they think it's going to work.&nbsp; More likely, ind=
ividual butterflies are predetermined to behave a certain way, and there is=
some variation between individuals.&nbsp; Often what we probably see is th=
at the strategy followed by most individuals in an area is the one that wor=
ks most of the time, and strategies followed by fewer individuals fail most=
of the time, but in some years these "failure" strategy followers are succ=
essful when the majority's strategy fails.&nbsp; The butterflies have no id=
ea whether their strategy will work.&nbsp; They just live their lives the w=
ay they are programmed to, and some survive while others do not.&nbsp; Thos=
e that survive pass their genes along to the next generation.<br /><br />He=
re's a completely made up example...<br /><br />There is a butterfly called=
the California Lady that ranges from the Bay Area to San Diego.&nbsp; Its =
native host plants are gumweeds.&nbsp; Now it turns out that gumweeds can s=
urvive the winter in San Diego, but in the SF Bay Area the winters are so c=
old that gumweeds only survive as seeds.&nbsp; Throughout their range, the =
butterflies can pass the winter as a caterpillar or an adult, but the cater=
pillars only make it if they have plenty of fresh gumweed to eat.&nbsp; And=
overwintering adults are highly prone to attack by ants as they hide out i=
n cracks and crevices to shelter against cold winter nights.&nbsp; <br /><b=
r />Now a detailed life history study from 1990-2000 found that in San Dieg=
o, 90% of individuals overwinter as caterpillars and 10% overwinter as adul=
ts.&nbsp; Once every decade, a very cold winter kills off the gumweed and t=
he overwintering caterpillars all starve to death, while some of the overwi=
ntering adults survive, despite many of them being eaten by ants.&nbsp; Eve=
n though overwintering as a caterpillar is the successful strategy in Sand =
Diego in most years, in very cold years the strategy of overwintering as an=
adult is what keeps the species from being wiped out locally.&nbsp; So it =
pays to have some outliers in the population, even though most years they f=
ail.<br /><br />The same 1990-2000 study found that SF Bay Area California =
Lady butterflies have the opposite strategy.&nbsp; 90% of individuals overw=
inter as adults and 10% as caterpillars.&nbsp; In 9 out of 10 winters, the =
cold weather kills off the gumweed and all the overwintering caterpillars s=
tarve to death.&nbsp; Only the overwintering adults survive the winter.&nbs=
p; But once per decade, an unusually warm winter allows the gumweed to live=
through the winter, and the overwintering caterpillars do much better than=
the overwintering adults, which get devoured by the ants, which are more a=
ctive than usual on the warmer nights.&nbsp; So here, overwintering as an a=
dult is usually the winning strategy, but in very warm years it's the overw=
intering caterpillars that keep the species from being wiped out locally.&n=
bsp; Again, it pays to have some outliers in the population, even though th=
ey fail in most years.<br /><br />The study was repeated in 2010-2020, but =
something had changed: Guernsey Gumweed was introduced to California and al=
though it did not do well in the face of competition from natives gumweeds =
in natural areas, it thrived in cities.&nbsp; The thing about Guernsey Gumw=
eed is that it does quite well in Bay Area winters.&nbsp; So what did the s=
tudy find?&nbsp; Things hadn't changed in San Diego: overwintering caterpil=
lars were still the most successful strategy in most years.&nbsp; And in na=
tural areas in the East Bay Hills, they found the same results as in the pr=
evious study: overwintering adults were the most successful in most years.&=
nbsp; But in SF where Guernsey Gumweed was well-established and supported c=
aterpillars through most winters, overwintering California Lady caterpillar=
s became the dominant strategy, just like in San Diego.&nbsp; <br /><br />T=
he study was then put on hold indefinitely because, after all, it was 2020.=
&nbsp; But then in 2100-2110 it was repeated.&nbsp; By then SF Bay area tem=
peratures had warmed by a few degrees, allowing native gumweeds to survive =
the winter in all but the coldest years.&nbsp; And in San Diego, winter tem=
peratures were so warm that gumweeds never died off, not even in the coldes=
t winters.&nbsp; So what did the study find?&nbsp; In San Diego, the overwi=
ntering adults had all but disappeared.&nbsp; Every individual found in win=
ter was a caterpillar.&nbsp; The same was true in SF, where the introduced =
Guernsey Gumweed supported overwintering caterpillars even through the cold=
est winters, and no overwintering adults could be found.&nbsp; What about i=
n the natural areas in the East Bay Hills, where the native gumweeds made i=
t through 9 out of 10 winters?&nbsp; There, the species had adopted the for=
mer San Diego scenario, in which 90% of California Ladies overwintered as c=
aterpillars and only 10% as adults.&nbsp; <br /><br />Now, imagine if someo=
ne asked the question: Do California Ladies overwinter as caterpillars or a=
dults?&nbsp; The answer would depend not only on the location, but also the=
year.&nbsp; Even back in the 1990s, the answer depended on the year, with =
most years favoring overwintering caterpillars, but 1 out of 10 years favor=
ing overwintering adults.&nbsp; Also, if someone had seen a California Lady=
in San Diego in June of 1995 and asked whether its offspring would overwin=
ter as adults or caterpillars, you wouldn't have been able to answer defini=
tively, although you could have said that there's a 90% chance they will ov=
erwinter as caterpillars and a 10% chance they'll overwinter as adults.&nbs=
p; <br /><br />Now back to the real world: Do American Ladies in SF breed i=
n September?&nbsp; How many butterflies would we need to observe to answer =
that question, and over how many years?&nbsp; And if we had studied them in=
the East Bay Hills, could we apply our results to the same species living =
in SF?&nbsp; Or if we had studied them before the arrival of the non-native=
cudweed, would our results still apply after the cudweed had been establis=
hed for a while?&nbsp; Will our results still apply as average temperatures=
change?<br /><br />Forgetting all of that for a moment, there are other re=
asons why answering the "breeding season(s)" question may be difficult...<b=
r /><br />For butterflies with multiple generations per year (all Vanessas =
in SF?), the timing of those generations may vary each year, and they may n=
ot always be in sync.&nbsp; (The following example is made up.)&nbsp; Maybe=
one Vanessa species usually breeds in April (1st generation), June (2nd ge=
neration), and August (3rd generation), and then goes into reproductive dia=
pause until April.&nbsp; But in an especially warm year, maybe that's March=
, May, and July.&nbsp; And maybe some of those July butterflies do breed an=
d have a generation that emerges in September and then diapauses through th=
e winter.&nbsp; And maybe in a cold year they start in May and only get two=
generations in that year.&nbsp; <br /><br />Some butterflies have partial =
generations.&nbsp; For example, Sara Orange-tips apparently have a full gen=
eration that flies in early spring, and some of their offspring emerge in l=
ate spring while others wait until the following spring to emerge.&nbsp; So=
their "breeding periods" may be easy to identify, but only some individual=
s are breeding during the second breeding period.<br /><br />Butterflies ma=
y have their life histories in sync with the life history of their local ho=
st plant, which may vary over small geographic scales.&nbsp; For example, A=
nise Swallowtails living in towns have been shown to have modified the timi=
ng of their life history to match the timing of non-native Fennel, while An=
ise Swallowtails in nearby natural areas retain their natural phenology.&nb=
sp; So the breeding seasons of Anise Swallowtails can be different in areas=
just a few miles apart.&nbsp; <br /><br />And as another example, I suspec=
t that the Variable Checkerspots in my area have such a long flight season =
because their caterpillars feed on at least three different plants, each of=
which grows in a different microclimate and has a different phenology.&nbs=
p; So when defining the breeding season for this species, should we separat=
e out each host plant cohort, or should we just lump them all together?&nbs=
p; <br /><br />I don't have any real data on this, but I have wondered abou=
t the Red Admirals I can find hilltopping on just about any warm winter day=
.&nbsp; The purpose of hilltopping is mating.&nbsp; Males go to hilltops to=
wait for receptive females to arrive, and then they mate.&nbsp; So if I se=
e male Red Admirals on hilltops, it must be their breeding season, right?&n=
bsp; Maybe not.&nbsp; Perhaps males are just covering their bases: any day =
that's warm enough to fly, they'll head for a nearby hilltop just in case a=
receptive female might arrive.&nbsp; But maybe females won't emerge and he=
ad for hilltops until March.&nbsp; If that's the case, then even though mal=
es appear to be ready to breed all winter long, I don't think it's really b=
reeding season until receptive females join them.&nbsp; But let's remember =
that there are often some outliers that don't follow the "normal" pattern.&=
nbsp; What if 1% of females are receptive throughout the winter and will fl=
y to hilltops on warm winter days to mate?&nbsp; Does that 1% make winter i=
nto Red Admiral breeding season?&nbsp; What if 10% of female Red Admirals b=
reed in winter?&nbsp; 50%?&nbsp; How do we determine what percentage of but=
terflies in breeding status is required to call it breeding season?<br /><b=
r />These examples are meant to convey some of the complexities of determin=
ing the breeding season(s) of butterfly species.&nbsp; Every species is dif=
ferent, and there may be complications, variability, local variation, evolu=
tion, etc.&nbsp; And definitions of "breeding season" may not be as straigh=
tforward as we would hope.<br /><br />I hope this helps!&nbsp; <br /><br />=
I encourage folks to photograph butterflies nectaring, breeding, laying egg=
s, etc. and post their observations on iNaturalist.&nbsp; The more of these=
observations get posted, the more data will be available to investigate th=
ese kinds of questions.&nbsp; <br /><br />Thanks,<br /><br />Paul<br />-- <=
br />Paul G. Johnson<br />Paicines, CA<br /><a href=3D"mailto:pjpolliwog@ya=
hoo," target=3D"_blank" rel=3D"noopener"><pjpolliwog...></a>


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